Plug type electric fuse



Jan. 17, 1939. M, B d D 2,144,134

PLUG TYPE ELECTRIC FUSE Filed April 26, 1935 l'llll-llllll' IIIVIIJII% A MM Max:157

Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE PLUG TYPE ELECTRIC FUSE Application April 26, 1935, Serial No. 18,275

Claims.

This invention relates to fuses of the plug type comprising a chambered body containing the fusible element; a center terminal contact at one end of the plug, and an external screw-threaded 5 terminal shell which holds the fuse in its receptacle.

Plug type fuses with which this invention relates are sold in large quantities at low prices and must interrupt short circuit currents on the conductors they protect. Due to their small size and low selling price their successful design and profitable manufacture present problems of con siderable magnitude.

One of the objects of the present invention is the provision of a plug type fuse of such construction that the fusible element or link can be made shorter and thinner than heretofore-for the same current rating, thereby to enhance the ability of the fuse safely to interrupt short circuit currents without liberation of fire producing gases or the rupturing of the fuse body.

A further object of the invention resides in the reduction of manufacturing cost of the fuse plug by reducing the number of parts thereof and arranging them in such manner that their assembly is facilitated.

Plug fuses are commonly made with a shell carrying body closed at the bottom end which carries the center contact and open at the top end which is covered by a separate transparent cover plate. Fuses are also commonly made wherein the shell carrying body is made of some transparent material such as glass that has a solid top end and is open at the bottom end and my invention is more particularly concerned with this latter type of fuse. With this type of fuse it has been common heretofore to close the open bottom of the fuse casing or body with an insulating plate that carries the center contact and is held to the fuse body by the screw-threaded shell, the shell end of the fuse link being bent around the lower end of the fuse body and interposed between and soldered to the shell. With this construction two separate soldering operations are necessary, one to secure the fuse link to the center contact and another to subsequently secure the link to the terminal shell.

It is an object of the present invention to provide a fuse construction wherein the insulating 50 member that carries the center contact is fixed to the terminal shell, at least sufficiently securely to permit the parts to be handled as a unitary structure, and wherein the fuse link can be soldered both to the center contact and to the shell 55 as in efiect a single operation. This construction not only reduces the cost of manufacture of the fuse but also facilitates the assembly since the fuse link and its terminal members form in effect a unitary structure which necessitates only the application of the fuse body and the securing of 5 the metal shell against rotation to the fuse body to complete the fuse.

In a fuse of the character set forth the metal shell is provided with an end wall which overlies the open end of the plug body and has an 10 aperture in which an insulating bushing is frictionall'y or otherwise retained, the bushing carrying the center contact.

It is a further object of the present invention to support the end wall of the terminal shell 15 against deformation due to the contact pressure between the center contact of the fuse and the center contact of the receptacle in which the fuse is screwed, by providing the bushing with an outstanding flange or the like that is interposed between the end wall of the shell and the end of the plug body and in engagement with both, thereby to transmit the contact pressure directly to the screw-threaded portion of the shell, a part of the inner face of the end wall of the shell, however, being exposed to the interior of the receptacle so that the fuse link may be soldered thereto.

A further object of the invention is the pro vision of a plug fuse wherein the terminal shell has an end wall that overlies the end of the plug body and wherein the fuse link is more or less cl-shaped and has one end soldered to the center contact and the other end soldered to the inner face of the end wall.

A further object is generally to improve the construction of plug fuses.

Fig. 1 is an elevation of a fuse embodying the invention.

Fig. 2 is a section along line 22 of Fig. 1.

Fig. 3 is a sectional view taken along line 33 of Fig. 2.

Fig. 4 is a view similar to Fig. 3 but taken at right angles thereto along line 4-4 of Fig. 2.

Fig. 5 is a perspective view of the insulating bushing that carries the center contact of the fuse.

Fig. 6 is a perspective view of the terminal shell, bushing and fuse link assembly.

The plug fuse herein chosen to illustrate the invention comprises a cylindrical fuse body l0 having external screw-threads l2, an open bottom end 14 and a top wall [6 that forms a top closure for the interior fuse containing chamber IS. The top wall i6 is transparent and preferably is integral in effect with the remainder of the fuse body as by making the entire fuse body I of glass or other suitable transparent material.

The top of the fuse body is also provided with an outstanding flange 29 by which the fuse can be rotated readily into and out of a suit-able fuse receptacle.

The fuse includes a cylindrical metal terminal shell 22 having registering internal and external screw-threads, the shell being screw-threaded upon the screw-threads of the plug body over the open end thereof. The shell is provided at its inner end with an integral end wall 2% which overlies the open end is of the plug body and has a circular opening or perforation 26 which is coaxial with the axis of the plug body.

The fuse also includes a generally cylindrical insulating bushing 23 which is located mainly within the terminal shell 22 and upstands from the inner face of the end wall 24 thereof, the bushing having an outstanding flange at which is seated upon the inner face of the end wall. The bushing at its lower end is provided with 2. preferably conically shaped projection 32 that projects through the aperture 26 in the end wall of the shell and has its lower end terminated below the end wall. The diameter of the conical portion 32 at the base thereof or where the conical portion joins the flange 412 so closely corresponds to the diameter of the aperture 26 that the conical portion is a tight fit in the aperture and engages the terminal shell sufficiently firmly so that the bushing and the shell form in effect a unitary structure which can be handled as such. The bushing and the conical end thereof has an axial passage 3 therein in which the long solid shank 36 of a center contact member 38 is fixed, the contact member having an enlarged head t!) which overlies the end of the conical projection 32 and is adapted to engage a corresponding center contact of the fuse receptacle.

The peripheral part of the flange 32 is positioned under the inner end of the plug body l0 so that when the fuse is assembled the flange E2 is clamped between the end wall of the terminal shell and the inner end of the plug body. The flange serves to transmit the contact pressure between the contact member 38 and its cooperating receptacle contact member directly to the screwthreaded portion of the shell and thereby relieve the end wall of the shell from the contact pressure.

The inner end of the shank 36 of the'center contact terminates substantially flush with the bottom of an enlarged recess or fuse link passage 44 of the bushing, which passage is open at the top. The bushing is formed on' the outer side thereof with an open vertical link-receiving channel 54 having an expanded upper end 56 and communicating with a slot 51 formed in the flange 52 and thereby exposing a portion 24a of the inner face of the end wall of the terminal shell.

The fuse is provided with a fusible element or fuse link t6 composed preferably of a relatively thin strip of readily fusible metal, which with the present construction can be thinner than usual for a given capacity, having about in the middle thereof a portion of reduced cross section such as is provided, for instance, by the hole 38, see Fig. 6, at which the fuse melts or blows upon overload and thereby interrupts the continuity of the circuit between the center contact member and the terminal shell.

The fuse link 36 is formed into substantially U-shaped configuration thereby having the legs Mia and 46b and the intermediate member 460 in which the perforation 48 is located. The leg 46a is disposed Within the passage as and is fixed to and is electrically secured to the top end of the shank 36 of the center contact 38 by a mass of solder 50. The end of the other leg i812 depends downwardly between the bushing and the inner face of the plug body in the channel 54 and is secured to an exposed face 26a of the end wall 2Q by a mass of solder 52. The intermediate portion 350 of the fuse link is disposed above the top end of the bushing and under the transparent wall N3 of the plug body wherein the fusing portion of the fuse link is visible.

The bushing is provided with a shoulder 36 at the base of-the slot 57 which bears against the end wall 2 5 and thus prevents the escape of solder and gases through the middle opening 26 therethrough. 7

With this construction the soldering of both ends of the link can be facilitated since both ends of the fuse link and the center contact and shell wall are readily accessible. The fuse link and its terminals are thus joined in a unitary structure which is applied to the plug body by merely screwing the terminal shell onto the screw-. threads of the plug body.

The bushing isolates the two legs of the fuse link and hence renders it difficult for a circuit interrupting arc to be maintained therefrom.

The terminal shell is fixed against rotation to the plug body in any suitable manner. As herein shown one of the screw-threads of the plug body is mutilated or has a notch 58 and the shell is inwardly struck to provide an indentation 60 that is located in the notch.

It will be noted that the center contact 38 of the plug is materially longer than the contacts in common use, which are essentially tubular rivets, and that the shank 36 thereof is solid instead of hollow, as is common. The center contact thus has much more mass than the usual contact and hence has higher heat absorbing ability. The

fuse link 55 thus can have less mass than is usual with the tubular rivet type of center contact since heat is absorbed from the link by the solid contact. usual, there is less metal to be vaporized on heavy current and hence the work of circuit interruption is easier and less pressure is generated within the plug body. The link can also be shorter than the usual link by reason of the increased length of the center contact. The fuse is relatively freely venting, the gas passing out of the interior of the plug body, or the chamber l8, through the slot 5? in the flange 4D and thence between the screw threads of the body and shell.

I claim:

1. A plug fuse comprising a chambered plug body having an open bottom end and external screw threads, a screw-threaded terminal shell carried by the screw threads of said plug body and having a circumferentially continuous end wall which overlies the open end of the plug body, said end wall having an aperture in the middle thereof, an insulating bushing disposed within said terminal shell and having a projection which projects through and conforms to the outline of and is a close fit in said aperture, said bushing having an outstanding flange overlying and sealing said end wall aperture and clamped between said end wall and said plug body, a center contact in said bushing and the projection thereof,

Since the link can be thinner than.

an inverted U-shaped fuse link within the chamber of said plug body having one end within said bushing and soldered to said center contact and the other end disposed outside said bushing and extended through said flange and soldered to the inner face of said end wall, and means securing said terminal shell and plug body against relative rotation.

2. A plug fuse comprising a chambered plug body having an open bottom end, a screwthreaded terminal shell carried by said plug body and having an end wall which overlies said open end and 'said opening thereof, said end wall having an opening therethrough, an insulating member overlying a part only of an inner face of said end wall and exposing another part of said inner face to the interior of said chamber and clamped between said end wall and body, a center contact carried by said insulating member and extended through said wall aperture, and a fuse link in said chamber having one end soldered to said center contact and the other end soldered to an exposed portion of the inner face of said end wall, said insulating member having a projection which extends through and is a tight fit in said end wall aperture.

3. A plug fuse comprising a chambered plug body having a lower open end and a transparent wall at its upper end, a screw-threaded terminal shell carried by said plug body and having an end wall that confronts the lower end of said body, an insulating bushing carried by said terminal shell and upstanding within the chamber of said plug body, said bushing having an outstanding flange which overlies said end wall and is located between it and said lower plug end and has a notch therein which exposes a part of the inner face of said end wall to said plug chamber, a center contact carried by the lower end of said bushing, a passage extending from the upper end of said bushing downwardly therein to said center contact, a fuse link having one end extended into said passage and soldered to said center contact and having its other end extended downwardly beside the bushing and into said notch and soldered to the exposed part of the inner face of the end wall of said terminal shell, said bushing having a groove in its side wall in which said link is located, said groove opening into said notch, the groove at the top of the bushing being wider than said notch.

4. A plug fuse comprising a chambered body open at the bottom, a terminal shell on said body having an end wall which overlies the open bottom thereof, an insulated center contact, a U- shaped fuse link having its one leg soldered to said center contact and its other leg soldered to the inner face of said end wall, and an insulating barrier carried by said shell and surrounding the leg connected with said center contact.

5. A plug fuse comprising a chambered body, a terminal shell thereon having an end wall that overlies the chamber of said body, an insulating bushing projecting through said shell, said bushing having a passage in its end that is within said body and a channel in its side that opens to the inner face of said end wall, a center contact on the projecting part of said bushing, and a fuse link in said passage and channel and soldered to said center contact and end wall, said channel being enlarged at its end opposite said end wall.

MORRIS B. WOOD. 

